Windmills have the potential to provide cheap energy on a global scale, to raise the standard of living of poor communities, and to contribute significantly to the reduction of global warming. People all over the world can benefit from the use of electricity generated by windmills for heating homes, lighting and other household activities.
Large fields of windmills are capable of supplying big cities and entire regions with electricity. The electricity, in turn, can also be used to charge batteries used to power electric vehicles or to generate hydrogen gas to be used by vehicles.
Vertical axis windmills can be scaled to very large sizes that can generate more electrical power than other windmill designs. They can also have a very low cost of manufacture and can be built from lightweight low-cost materials. They can also generate electricity even if the speed of wind is extremely low or almost at a standstill when other common windmill designs are unable to generate power at all. They are omnidirectional in the sense that they do not have to be oriented relative to the wind and can operate equally well for any wind direction or indeed under conditions of rapidly changing wind direction. Various designs for vertical axis windmills have been proposed including that disclosed in co-pending U.S. patent application Ser. No. 11/790,494, which is incorporated herein by reference, as well as earlier designs by Weaver (U.S. Pat. No. 1,286,853), Decker (U.S. Pat. No. 3,920,354), and Zukeran (U.S. Pat. No. 4,365,935).
An important feature of any useful large vertical axis windmill design is a safety mechanism for overspeed protection in high winds. The above mentioned application and patents disclose various mechanical mechanisms for this purpose. For example, co-pending U.S. patent application Ser. No. 11/790,494 discloses movable horizontal bars that stop a plurality of lightweight sail elements. At low wind speed, these movable horizontal bars block the lightweight sail elements such that the full force of available wind can be brought to bear against the full area of each sail element. As the wind speed increases above a pre-determined threshold, the movable horizontal bars are pushed away from the plane of the main sail frames such that a portion of the wind is allowed to leak through, thereby reducing the amount of force applied to each sail element. A suitable maximum power output can continue to be collected, the windmill structure is protected from damage due to excessive force, and it is not necessary to shut down the windmill, no matter how much the wind speed increases.
Zukeran discloses a different protection mechanism depending solely on gravity. The sail elements are the full size of the frames and are mounted inside weighted frames which can swing in the downwind direction when the wind is fast enough to provide enough deflection force to lift the weights.